mi 
in the Island St Michael. 
ceous sinter, which is most abundant in St Michael, is in layers 
from a quarter to a half inch in thickness , which are accumu- 
lated on each other, to the height often of a foot and upwards, 
constituting distinct and wide strata, many yards in extent. 
These strata are always parallel, and for the most part horizon- 
tal, but in some places they are slightly undulating. Between 
the layers of this substance is a loose white powder, which, on 
examination, is found to be nearly pure silex, with a small pro- 
portion of alumina. When moist, it is nearly gelatinous. The 
colour of the slaty variety is pearl-grey ; externally it is dull, 
but on the fresh fracture has a glistening lustre, and is trans- 
lucent on the edges. The fracture is nearly smooth, inclining a 
little to conchoidal. It scratches glass with ease, and has a speci- 
fic gravity of 2.107. It is infusible before the common blowpipe. 
Another variety of sinter has a snow-white colour, and is ex- 
ternally wrinkled, abounding in slight depressions and protu- 
berances, which are almost circular. This is found in delicate 
crusts, and often covers irregularly shaped masses of the other 
varieties. It has a very beautiful semi-opalescent lustre. The 
crusts are brittle, and seldom exceed the tenth of an inch in 
thickness. Their specific gravity is 1.886. Upon masses of a 
kind of conglomerate of altered lava and pumice, I noticed a 
very beautiful variety of Fiorite, in small circular cup-shaped 
portions, the edges of which are of a pure flesh-red, becoming 
gradually fainter, till the centres are perfectly snow-white. 
Another variety has the following characters : its colour is 
snow-white, reddish and yellowish-white, passing, in some spe- 
cimens, to yellowish-grey. It occurs in long, slender, capil- 
lary filaments, from one to four inches in length. The fila- 
ments cross each other in every direction. On the cross frac- 
ture, viewed with a microscope, a lustre between vitreous and 
pearly is observed. It is translucent, brittle, and light. When 
reduced to powder, and rubbed over the surface of a plate of 
glass, it scratches it. Its specific gravity is 1 .866. It is in- 
soluble in nitric, muriatic, or sulphuric acids, and is infusible 
before Brooke’s blowpipe. A portion of this mineral was exa- 
the Royal Society of Edinburgh ; but I recollect no specimens of siliceous sinter, 
which equal in beauty some of those from St Michael. 
